The customer details are put into the customer database table automatically after a transaction is processed. The Add/Edit Customers menu allows you to modify the details of an existing customer or manually add a new customer to the database. You can also delete a customer from the database if you want (for example after you give him a refund).

WP eStore Add/Edit Customer Screen
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@Pee, This information is collected from PayPal (this way all the information is valid information). This also makes it so the checkout process is much faster with lower cart abandon rate. All this information is automatically saved in the database after the transaction is complete and verified as a paid transaction.
I’ve got a question,
How are this info gathered? Was it based on the PayPal Process gateway? Then it’s automatically saved on Manage Customers Menu?
Thanks, for the very useful info. I will apply this to my website.